Modified positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, and discloses a modified positive electrode material and a preparation method and application thereof.The preparation method comprises the following steps that 1, a sodium source, a nickel source, an iron source and a manganese source are subjected to first mixing and then sintered, and a first intermediate product is obtained; (2) carrying out second mixing on the first intermediate product and nano zinc powder, and annealing to obtain a second intermediate product; and (3) carrying out third mixing on the second intermediate product and an organic carbon source solution, and then sequentially carrying out hydrothermal reaction and carbonization to obtain the modified positive electrode material. The preparation method comprises the following steps: mixing a material containing nickel, iron and manganese elements with nano zinc powder, annealing to form nano zinc metal net-shaped doping, and then carrying out hydrothermal reaction and carbonization process on the nano zinc metal net-shaped doping and an organic carbon source solution to obtain the modified positive electrode material with the inner net-shaped doping and the surface coated with a graphitized carbon layer. And the conductivity, the structural stability and the interface compatibility of the sodium electric material are improved, so that the comprehensive electrochemical performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of batteries, specifically to a modified cathode material, its preparation method, and its application. Background Technology

[0002] With the continuous growth of global energy demand and increasing emphasis on environmental protection, the development of energy storage technology has become crucial. Sodium-ion batteries, due to their abundant resources, low cost, and high safety, have become an important research direction in the energy storage field, and the cathode material is one of the key factors in the performance of sodium-ion batteries. Currently, in the research of cathode materials for sodium-ion batteries, layered transition metal oxides (Na₂O₃) are being studied. x TMO2 has attracted much attention, where TM represents transition metal elements (such as Ni, Fe, Mn, and Co). Among existing methods for preparing sodium-ion battery cathode materials, the high-temperature solid-state method involves mixing metal oxides with a sodium source in a stoichiometric ratio and then calcining at high temperatures (800-1000℃) to allow solid-state ion diffusion to form the target product. This method has the advantages of simple processing and suitability for large-scale production, but the sodium element distribution in the synthesized material is uneven, and it is difficult to precisely control the particle size and morphology, thus presenting certain limitations. Sodium manganate (NaMnO2) cathode materials, as typical layered oxide cathode materials, are considered one of the most promising candidate materials for sodium-ion battery cathodes due to their high theoretical specific capacity, moderate operating voltage, and simple preparation process.

[0003] Currently, sodium-ion battery cathode materials mainly face the following technical challenges: First, low conductivity: the electronic conductivity network of layered oxides is imperfect, which limits the rate performance; second, poor structural stability: during high-voltage cycling, Mn-based materials are prone to Mn dissolution and structural collapse, leading to capacity decay; third, easy occurrence of interfacial side reactions: the contact surface between the cathode material and the electrolyte has high activity, which easily generates by-products and reduces coulombic efficiency.

[0004] In recent years, significant progress has been made in the modification of sodium manganate-based cathode materials. Methods such as Na-site doping with Li / K, Mn-site doping with Fe / Co / Ni, and O-site doping with F / S can broaden sodium ion diffusion channels and suppress phase transitions. Surface modification with materials such as TiO2, Al2O3, and carbon nanotubes can construct physical barriers to reduce manganese leaching. While these technologies alleviate conductivity and structural issues to some extent, they still suffer from drawbacks such as cost, process complexity, and less-than-ideal cycle life. Furthermore, manganese ions in sodium manganate-based cathode materials readily dissolve in the electrolyte and migrate to the negative electrode, forming metal deposits. This leads to voltage hysteresis, reduced reversible capacity, and high activity at the interface between the cathode material and the electrolyte, easily generating byproducts and degrading battery cycle performance. Summary of the Invention

[0005] This invention provides a modified cathode material, its preparation method, and its application to solve the problems of low conductivity, poor structural stability, and poor interfacial compatibility of sodium manganate-based cathode materials, which lead to low overall electrochemical performance of sodium-ion batteries.

[0006] In a first aspect, the present invention provides a method for preparing a modified cathode material, comprising the following steps: (1) Sodium source, nickel source, iron source and manganese source are mixed for the first time, and then sintered to obtain the first intermediate product; (2) The first intermediate product is mixed with nano zinc powder for a second time, and then annealed to obtain the second intermediate product; (3) The second intermediate product is mixed with the organic carbon source solution in a third mixing process, and then subjected to hydrothermal reaction and carbonization in sequence to obtain the modified cathode material.

[0007] In an optional implementation, the molar ratio of sodium in the sodium source, nickel in the nickel source, iron in the iron source and manganese in the manganese source in step (1) is x:a:b:c, where 0 < x ≤ 0.85, 0 < a < 0.2, 0 < b < 0.1, 0 < c < 0.75, and a + b + c < 1.

[0008] Optionally, the sodium source includes at least one of sodium carbonate (Na2CO3), sodium nitrate (NaNO3), sodium sulfate (Na2SO4), sodium acetate (CH3COONa), and sodium chloride (NaCl).

[0009] Optionally, the nickel source includes at least one of nickel oxide (NiO), nickel carbonate (NiCO3), nickel nitrate (Ni(NO3)2), nickel sulfate (NiSO4), and nickel acetate (Ni(CH3COO)2).

[0010] Optionally, the iron source includes at least one of iron oxide (Fe2O3), iron carbonate (Fe2(CO3)3), iron nitrate (Fe(NO3)3), and iron sulfate (Fe2(SO4)3).

[0011] Optionally, the manganese source includes at least one of manganese oxide (MnO2), manganese carbonate (MnCO3), manganese nitrate (Mn(NO3)2), and manganese sulfate (MnSO4).

[0012] In an optional implementation, a dispersant is also added during the first mixing process in step (1).

[0013] Furthermore, in an optional embodiment, the dispersant comprises polyvinyl alcohol.

[0014] Further, in an optional embodiment, the mass ratio of the dispersant to the total mass of the sodium source, nickel source, iron source and manganese source is (3-10):(90-97).

[0015] In an optional implementation, the rotational speed of the first mixing in step (1) is 200-500 rpm.

[0016] In an optional implementation, the mixing time in step (1) is 10-15 hours.

[0017] Optionally, the first mixing method is ball milling, which is carried out in a stainless steel ball milling jar, and the ball milling media used has a particle size of 5-20 mm.

[0018] In an optional implementation, the sintering in step (1) includes a first sintering stage and a second sintering stage performed sequentially.

[0019] Furthermore, in an optional embodiment, the heating rate of the first sintering stage is 1-5°C / min.

[0020] Furthermore, in an optional embodiment, the holding temperature of the first sintering stage is 400-600°C.

[0021] Furthermore, in an optional embodiment, the holding time for the first sintering stage is 1-3 hours.

[0022] Furthermore, in an optional embodiment, the heating rate of the second sintering stage is 1-5°C / min.

[0023] Furthermore, in an optional embodiment, the holding temperature of the second sintering stage is 920-980°C.

[0024] Furthermore, in an optional embodiment, the holding time for the second sintering stage is 5-10 hours.

[0025] Furthermore, in an optional embodiment, the atmospheres of the first sintering stage and the second sintering stage are independently selected from oxygen-containing atmospheres.

[0026] Optionally, the gas in the oxygen-containing atmosphere used in the sintering process includes compressed air or an oxygen atmosphere.

[0027] In an optional embodiment, the average particle size of the nano zinc powder in step (2) is 15-40 nm.

[0028] In an optional implementation, the ratio of the total molar amount of nickel, iron and manganese in the first intermediate product to the molar amount of zinc in the nano zinc powder in step (2) is (a+b+c):d, where d=1-abc, 0<d≤0.2.

[0029] In an optional implementation, the rotational speed of the second mixing in step (2) is 500-800 rpm.

[0030] In an optional implementation, the mixing time in step (2) is 3-5 hours.

[0031] Optionally, step (2) of the second mixing method includes ball milling.

[0032] In an optional implementation, the annealing in step (2) is performed at a heating rate of 1-5 °C / min.

[0033] In an optional implementation, the holding temperature for annealing in step (2) is 700-900°C.

[0034] In one optional implementation, the annealing holding time in step (2) is 4-6 hours.

[0035] In an optional embodiment, the organic carbon source in the organic carbon source solution in step (3) includes at least one of glucose, phenolic resin, and sucrose.

[0036] In an optional embodiment, the concentration of the organic carbon source solution in step (3) is 0.1-1 mol / L.

[0037] In an optional embodiment, the mass ratio of the second intermediate product to the organic carbon source solution in step (3) is 1:(1-3).

[0038] In an optional implementation, the temperature of the hydrothermal reaction in step (3) is 150-200°C.

[0039] In an optional implementation, the hydrothermal reaction time in step (3) is 10-15 hours.

[0040] In an optional implementation, the carbonization temperature in step (3) is 550-800°C.

[0041] In an optional implementation, the carbonization time in step (3) is 3-5 hours.

[0042] In an optional implementation, the carbonization atmosphere in step (3) includes a nitrogen atmosphere or an inert atmosphere.

[0043] Optionally, the purity of the nitrogen atmosphere is >98%.

[0044] Optionally, the inert atmosphere includes at least one of argon, helium, and neon atmospheres.

[0045] In a second aspect, the present invention provides a modified cathode material, which is prepared by the preparation method described in the first aspect. The modified cathode material includes a matrix material and a carbon coating layer covering the surface of the matrix material. The matrix material includes sodium, nickel, iron, manganese and zinc. The zinc in the modified cathode material is doped in a nano-network structure.

[0046] In an optional embodiment, the matrix material has the chemical formula Na. x Ni a Fe b Mn c Zn d O2, where 0 < x ≤ 0.85, 0 < a < 0.20, 0 < b < 0.10, 0 < c < 0.75, 0 < d ≤ 0.2, and d = 1 - abc.

[0047] In one optional embodiment, the carbon material in the carbon coating layer is graphitized carbon material.

[0048] Thirdly, the present invention provides a sodium-ion battery, the sodium-ion battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode material, the positive electrode material comprising the modified positive electrode material described in the second aspect.

[0049] The technical solution of this invention has the following advantages: 1. The method for preparing the modified cathode material provided by the present invention includes the following steps: (1) mixing sodium source, nickel source, iron source and manganese source in a first mixing and then sintering to obtain a first intermediate product; (2) mixing the first intermediate product with nano zinc powder in a second mixing and then annealing to obtain a second intermediate product; (3) mixing the second intermediate product with an organic carbon source solution in a third mixing and then sequentially undergoing hydrothermal reaction and carbonization to obtain the modified cathode material. The preparation method provided by this invention involves mixing and annealing an intermediate product containing nickel, iron, and manganese with nano-zinc powder to form nano-zinc doping in a sodium-ion battery cathode material. During the doping process, the nano-zinc powder can construct a highly conductive network structure. The introduced zinc atoms form chemical bonds Zn-O with the functional groups in the first intermediate product. The Zn-O bonds can provide zinc affinity sites with high affinity, promoting more uniform zinc formation at these sites, inhibiting dendrite growth, and improving the structural stability of the resulting cathode material. At the same time, zinc doping can also improve the ion / electron transport characteristics of the resulting sodium-ion battery cathode material, realizing a multiple modification mechanism of optimizing ion channels, enhancing structural stability, and reducing interfacial impedance, significantly improving the cycle stability and rate performance of the sodium-ion battery cathode material. Next, a continuous carbon gel coating layer is formed on the surface of the nano-zinc mesh-doped sodium-ion cathode material through a hydrothermal reaction with an organic carbon source solution. During high-temperature carbonization, the carbon gel coating layer formed by the hydrothermal reaction can be transformed into a graphitized structure. By performing the hydrothermal reaction process before carbonization, the local aggregation of carbon materials and a large number of porous copper structures that occur during high-temperature carbonization can be avoided, making the coating layer more uniform and dense. Furthermore, the hydrothermal-carbonization two-step method can also construct a three-dimensional conductive network structure on the surface of the doped sodium-ion cathode material, thereby further improving the electronic conductivity of the sodium-ion cathode material and reducing the charge transfer impedance. In addition, the graphitized carbon layer can also suppress the volume expansion and structural damage of the cathode material during battery charging and discharging, and promote the formation of a stable solid electrolyte interphase (SEI) film, thereby improving the cycle life, capacity performance and cycle stability of the battery.

[0050] This invention involves mixing sodium-ion battery materials containing nickel, iron, and manganese with nano-zinc powder and then annealing the mixture to form a nano-zinc metal mesh-doped sodium-ion battery cathode material. This material is then subjected to a hydrothermal reaction and carbonization process with an organic carbon source solution to obtain a modified cathode material with internal mesh doping and a graphitized carbon layer coating on the surface. Through the combined effect of the above processes, the conductivity, structural stability, and interfacial compatibility of the modified cathode material are improved, thereby enhancing the overall electrochemical performance of sodium-ion batteries. Attached Figure Description

[0051] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0052] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the modified cathode material prepared by the preparation method provided in Example 1 of this invention. Detailed Implementation

[0053] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0054] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0055] Example 1 This embodiment provides a method for preparing a modified cathode material, including the following steps: (1) Na2CO3, NiO, Fe2O3 and MnO2 were mixed with polyvinyl alcohol (PVA) in a molar ratio of sodium, nickel, iron and manganese of 0.8:0.15:0.05:0.7. The mass ratio of PVA to the total mass of Na2CO3, NiO, Fe2O3 and MnO2 was 5:95. The first mixture was ball-milled in a stainless steel ball mill jar. The ball milling media used in the first ball mill was zirconia balls with a particle size of 10 mm. The speed of the first ball mill was 300 rpm and the time of the first ball mill was 12 h. Then, the product obtained after the first ball milling was placed in a tube furnace. In the atmosphere of compressed air, the temperature was first raised to 500℃ at a heating rate of 2℃ / min and held for 2 h, and then raised to 950℃ at a heating rate of 2℃ / min and held for 6 h to obtain the first intermediate product.

[0056] (2) The first intermediate product obtained in step (1) is mixed with the nano zinc powder by a second ball milling at a speed of 600 rpm for 4 h. Then, the product obtained by the second ball milling is placed in a tube furnace and annealed at 800 ℃ for 5 h in a compressed air atmosphere at a heating rate of 2 ℃ / min to obtain the second intermediate product. The zinc element in the second intermediate product is doped in a metal mesh structure. The average particle size of the nano zinc powder is 30 nm. The ratio of the total molar amount of nickel, iron and manganese elements in the first intermediate product to the molar amount of zinc element in the nano zinc powder is 0.9:0.1.

[0057] (3) The second intermediate product obtained in step (2) is mixed with a glucose solution with a concentration of 0.5 mol / L. The mass ratio of the second intermediate product to the glucose solution is 1:2. The mixed product is subjected to hydrothermal reaction at 180°C for 12 h. Then, the product obtained from the hydrothermal reaction is carbonized at 700°C for 4 h in a N2 atmosphere with a purity of 99% to prepare the modified cathode material.

[0058] The modified cathode material prepared by the above-described preparation method in this embodiment includes a matrix material and a carbon coating layer on the surface of the matrix material. The chemical formula of the matrix material is Na. 0.8 Ni 0.15 Fe 0.05 Mn 0.7 Zn 0.1 In the modified cathode material, zinc is doped in a nano-network structure, and the carbon material in the carbon coating layer is graphitized carbon material.

[0059] Example 2 This embodiment provides a method for preparing a modified cathode material, including the following steps: (1) Na2CO3, NiO, Fe2O3 and MnO2 were mixed with polyvinyl alcohol (PVA) in a molar ratio of sodium, nickel, iron and manganese of 0.85:0.1:0.09:0.74. The mass ratio of PVA to the total mass of Na2CO3, NiO, Fe2O3 and MnO2 was 10:90. The first mixture was ball-milled in a stainless steel ball mill jar. The ball milling media used in the first ball mill was zirconia balls with a particle size of 10 mm. The speed of the first ball mill was 200 rpm and the time of the first ball mill was 15 h. Then, the product obtained after the first ball milling was placed in a tube furnace. In the atmosphere of compressed air, the temperature was first raised to 400℃ at a heating rate of 5℃ / min and held for 3 h, and then raised to 980℃ at a heating rate of 5℃ / min and held for 5 h to obtain the first intermediate product.

[0060] (2) The first intermediate product obtained in step (1) is mixed with the nano zinc powder by a second ball mill at a speed of 500 rpm for 3 h. Then, the product obtained by the second ball mill is placed in a tube furnace and annealed at 900 °C for 4 h in a compressed air atmosphere at a heating rate of 5 °C / min to obtain the second intermediate product. The zinc element in the second intermediate product is doped in a metal mesh structure. The average particle size of the nano zinc powder is 15 nm. The ratio of the total molar amount of nickel, iron and manganese elements in the first intermediate product to the molar amount of zinc element in the nano zinc powder is 0.93:0.07.

[0061] (3) The second intermediate product obtained in step (2) is mixed with a glucose solution with a concentration of 0.1 mol / L. The mass ratio of the second intermediate product to the glucose solution is 1:1. The mixed product is subjected to hydrothermal reaction at 200°C for 10 h. Then, the product obtained from the hydrothermal reaction is carbonized at 800°C for 3 h in a N2 atmosphere with a purity of 99% to prepare the modified cathode material.

[0062] The modified cathode material prepared by the above-described preparation method in this embodiment includes a matrix material and a carbon coating layer on the surface of the matrix material. The chemical formula of the matrix material is Na. 0.85 Ni 0.1 Fe 0.09 Mn 0.74 Zn 0.07 In the modified cathode material, zinc is doped in a nano-network structure, and the carbon material in the carbon coating layer is graphitized carbon material.

[0063] Example 3 This embodiment provides a method for preparing a modified cathode material, including the following steps: (1) Na2CO3, NiO, Fe2O3 and MnO2 were mixed with polyvinyl alcohol (PVA) in a molar ratio of sodium, nickel, iron and manganese of 0.7:0.18:0.02:0.6. The mass ratio of PVA to the total mass of Na2CO3, NiO, Fe2O3 and MnO2 was 3:97. The first mixture was ball-milled in a stainless steel ball mill jar. The ball milling media used in the first ball mill was zirconia balls with a particle size of 10 mm. The speed of the first ball mill was 500 rpm and the time of the first ball mill was 10 h. Then, the product obtained after the first ball milling was placed in a tube furnace. In the atmosphere of compressed air, the temperature was first raised to 600℃ at a heating rate of 1℃ / min and held for 1 h, and then raised to 920℃ at a heating rate of 1℃ / min and held for 10 h to obtain the first intermediate product.

[0064] (2) The first intermediate product obtained in step (1) is mixed with the nano zinc powder by a second ball milling at a speed of 800 rpm for 5 h. Then, the product obtained by the second ball milling is placed in a tube furnace and annealed at 700°C for 6 h in a compressed air atmosphere at a heating rate of 1°C / min to obtain the second intermediate product. The zinc element in the second intermediate product is doped in a metal mesh structure. The average particle size of the nano zinc powder is 40 nm. The ratio of the total molar amount of nickel, iron and manganese elements in the first intermediate product to the molar amount of zinc element in the nano zinc powder is 0.8:0.2.

[0065] (3) The second intermediate product obtained in step (2) is mixed with a glucose solution with a concentration of 1 mol / L. The mass ratio of the second intermediate product to the glucose solution is 1:3. The mixed product is subjected to hydrothermal reaction at 150°C for 15 h. Then, the product obtained from the hydrothermal reaction is carbonized at 550°C for 5 h under a N2 atmosphere with a purity of 99% to prepare the modified cathode material.

[0066] The modified cathode material prepared by the above-described preparation method in this embodiment includes a matrix material and a carbon coating layer on the surface of the matrix material. The chemical formula of the matrix material is Na. 0.7 Ni 0.18 Fe 0.02 Mn 0.6 Zn 0.2 In the modified cathode material, zinc is doped in a nano-network structure, and the carbon material in the carbon coating layer is graphitized carbon material.

[0067] Example 4 The only difference between this embodiment and Embodiment 1 is that the addition of polyvinyl alcohol is omitted in step (1). All other contents are the same as in Embodiment 1.

[0068] Example 5 The only difference between this embodiment and Embodiment 1 is that step (1) omits the process of heating to 500°C at a heating rate of 2°C / min and holding for 2 hours. Instead, the product obtained after the first ball milling is directly heated to 950°C at a heating rate of 2°C / min and held for 6 hours in a compressed air atmosphere. All other contents are the same as in Embodiment 1.

[0069] Example 6 The only difference between this embodiment and Embodiment 1 is that step (1) omits the sintering process of heating to 950°C at a heating rate of 2°C / min and holding for 6 hours, and instead heats the product obtained after the first ball milling to 500°C at a heating rate of 2°C / min and holds for 2 hours in a compressed air atmosphere. All other contents are the same as in Embodiment 1.

[0070] Example 7 The only difference between this embodiment and Embodiment 1 is that the average particle size of the nano zinc powder used in step (2) is 10 nm. All other contents are the same as in Embodiment 1.

[0071] Example 8 The only difference between this embodiment and Embodiment 1 is that the average particle size of the nano zinc powder used in step (2) is 45 nm. All other contents are the same as in Embodiment 1.

[0072] Example 9 The only difference between this embodiment and Example 1 is that: in step (1), the molar ratio of sodium, nickel, iron, and manganese is 0.8:0.12:0.03:0.55; and in step (2), the ratio of the total molar amount of nickel, iron, and manganese in the first intermediate product to the molar amount of zinc in the nano zinc powder is 0.7:0.3. Accordingly, the chemical formula of the matrix material in the obtained modified cathode material is Na. 0.8 Ni 0.12 Fe 0.03 Mn 0.55 Zn 0.3 O2. All other contents are the same as in Example 1.

[0073] Example 10 The only difference between this embodiment and Example 1 is that the concentration of the glucose solution in step (3) is 0.05 mol / L. All other contents are the same as in Example 1.

[0074] Example 11 The only difference between this embodiment and Example 1 is that the concentration of the glucose solution in step (3) is 1.5 mol / L. All other contents are the same as in Example 1.

[0075] Comparative Example 1 The only difference between this comparative example and Example 1 is that: all the processes in step (3) are omitted, the product obtained in step (2) is not carbon-coated, and Na is directly prepared through steps (1) and (2). 0.8 Ni 0.15 Fe 0.05 Mn 0.7 Zn 0.1 O2. All other contents are the same as in Example 1.

[0076] Comparative Example 2 The only difference between this comparative example and Example 1 is that: all the processes in step (2) are omitted, the doping of the nano zinc powder network structure is not performed, and the first intermediate product obtained in step (1) is directly mixed with glucose solution in step (3), and then subjected to hydrothermal reaction and carbonization processes in sequence to obtain the modified cathode material. All other contents are the same as in Example 1.

[0077] Comparative Example 3 The only difference between this comparative example and Example 1 is that the process in step (3) is replaced by directly mixing the second intermediate product obtained in step (2) with glucose (solid), and then carbonizing the mixed product at 700°C for 4 hours under a N2 atmosphere to form a modified cathode material. All other contents are the same as in Example 1.

[0078] Comparative Example 4 The only difference between this comparative example and Example 1 is that the nano zinc powder in step (2) is replaced with zinc sulfide (ZnS) with the same molar amount of zinc. All other contents are the same as in Example 1.

[0079] Comparative Example 5 The only difference between this comparative example and Example 1 is that the nano zinc powder in step (2) is replaced with zinc oxalate with the same molar amount of zinc. All other contents are the same as in Example 1.

[0080] Comparative Example 6 The only difference between this comparative example and Example 1 is that the nano zinc powder in step (2) is replaced with zinc oxide (ZnO) with the same molar amount of zinc. All other contents are the same as in Example 1.

[0081] The modified cathode materials prepared in the above examples and comparative examples were used to prepare coin cells. The specific preparation method was as follows: the modified cathode materials prepared in the above examples and comparative examples, polyvinylidene fluoride (PVDF) and conductive agent acetylene black were mixed in a mass ratio of 95:2.5:2.5, and N-methylpyrrolidone was added for homogenization to obtain a cathode slurry. The cathode slurry was coated onto the surface of a current collector (aluminum foil) to form a cathode sheet. Sodium metal was used as the counter electrode, glass fiber was used as the separator, and the electrolyte was a 1 mol / L NaPF6 solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC to DMC volume ratio 1:1). In an argon glove box (where water <0.01 ppm and oxygen <0.01 ppm), the cathode sheet, counter electrode, separator gasket and spring were assembled into a CR2032 coin cell. Finally, the battery was placed in the Blue Electric Test System for electrical performance testing. The electrical performance test conditions are as follows: charge / discharge voltage range 2.5V-4.1V, test temperature 25℃. The battery's initial charge / discharge performance is tested after one cycle at 0.1C / 0.1C. Then, the battery is cycled sequentially at 0.2C / 0.2C, 0.5C / 0.5C, and 1C / 1C. The battery is cycled once at 0.2C / 0.2C, once at 0.5C / 0.5C, and 50 times at 1C / 1C. The initial discharge specific capacity at 0.1C / 0.1C is recorded. The rate performance (%) is calculated as follows: (initial discharge capacity at 1C / 1C) ÷ (initial discharge capacity at 0.1C / 0.1C). The capacity retention rate (%) after 50 cycles at 1C / 1C is calculated as follows: discharge capacity after the 50th cycle at 1C / discharge capacity of the first cycle at 1C.

[0082] The test results are shown in Table 1: Table 1

[0083] As shown in Table 1, this invention mixes sodium-ion battery materials containing nickel, iron, and manganese with nano-zinc powder and then anneals them to form a nano-zinc metal mesh-doped sodium-ion battery cathode material. This material is then subjected to a hydrothermal reaction and carbonization process with an organic carbon source solution to obtain a modified cathode material with internal mesh doping and a graphitized carbon layer coating on the surface. Through the combined effect of the above processes, the conductivity, structural stability, and interfacial compatibility of the modified cathode material are improved, thereby enhancing the overall electrochemical performance of the sodium-ion battery.

[0084] Figure 1 This is the X-ray diffraction pattern of the modified cathode material prepared by the preparation method provided in Example 1 of this invention. As can be seen from the figure, the modified cathode material prepared by the preparation method provided in Example 1 has a sodium-electric layered oxide structure, and at 43... ° ~44 °The presence of distinct diffraction peaks within the range indicates that zinc has been incorporated into the cathode material.

[0085] Compared with Example 1, Comparative Example 1 omits step (3) of mixing with organic carbon source solution, hydrothermal reaction and carbonization process, which will result in the inability to effectively improve the electronic conductivity of modified cathode material and the decrease in structural stability of modified cathode material during cycling, thereby reducing the capacity performance, rate performance and cycle stability of sodium-ion battery, and thus the overall performance of battery deteriorates.

[0086] Compared with Example 1, the doping process of the nano zinc powder in Comparative Example 2, which omits step (2), will result in the inability to simultaneously optimize ion channels, enhance structural stability and reduce interface impedance, thereby causing a significant decrease in the battery's capacity performance, rate performance and capacity retention.

[0087] Compared with Example 1, Comparative Example 3 directly mixed the second intermediate product with glucose in a solid phase without omitting the hydrothermal reaction, which caused the carbon material after direct carbonization to locally aggregate and generate a porous structure, resulting in a significant decrease in the density and uniformity of the coating layer, thereby significantly deteriorating the overall electrochemical performance of the battery.

[0088] Compared with Example 1, Comparative Examples 4-6 replaced the nano zinc powder with zinc sulfide, zinc oxalate and zinc oxide, which resulted in the inability to achieve the doping of the nano zinc network structure. This led to a decrease in the structural stability and conductivity of the obtained modified cathode material, which in turn resulted in a deterioration in the cycle stability, rate performance and capacity performance of the sodium-ion battery.

[0089] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a modified cathode material, characterized in that, Includes the following steps: (1) Sodium source, nickel source, iron source and manganese source are mixed for the first time, and then sintered to obtain the first intermediate product; (2) The first intermediate product is mixed with nano zinc powder for a second time, and then annealed to obtain the second intermediate product; (3) The second intermediate product is mixed with the organic carbon source solution in a third mixing process, and then subjected to hydrothermal reaction and carbonization in sequence to obtain the modified cathode material.

2. The method for preparing the modified cathode material according to claim 1, characterized in that, The molar ratio of sodium in the sodium source, nickel in the nickel source, iron in the iron source and manganese in the manganese source in step (1) is x:a:b:c, where 0<x≤0.85, 0<a<0.2, 0<b<0.1, 0<c<0.75, and a+b+c<1. And / or, in step (1), a dispersant is also added during the first mixing process; Preferably, the dispersant comprises polyvinyl alcohol; Preferably, the ratio of the mass of the dispersant to the total mass of the sodium source, nickel source, iron source and manganese source is (3-10):(90-97).

3. The method for preparing the modified cathode material according to claim 1 or 2, characterized in that, Step (1) The rotation speed of the first mixing is 200-500 rpm; And / or, the time for the first mixing in step (1) is 10-15 hours; And / or, the sintering in step (1) includes a first sintering stage and a second sintering stage performed sequentially.

4. The method for preparing the modified cathode material according to claim 3, characterized in that, The heating rate in the first sintering stage is 1-5℃ / min; Preferably, the holding temperature during the first sintering stage is 400-600℃; Preferably, the holding time in the first sintering stage is 1-3 hours; Preferably, the heating rate in the second sintering stage is 1-5℃ / min; Preferably, the holding temperature during the second sintering stage is 920-980℃; Preferably, the holding time in the second sintering stage is 5-10 hours; Preferably, the atmospheres of the first sintering stage and the second sintering stage are independently selected from oxygen-containing atmospheres.

5. The method for preparing the modified cathode material according to any one of claims 1-4, characterized in that, The average particle size of the nano zinc powder in step (2) is 15-40 nm; And / or, in step (2), the ratio of the total molar amount of nickel, iron and manganese in the first intermediate product to the molar amount of zinc in the nano zinc powder is (a+b+c):d, where d=1-abc, 0<d≤0.2; And / or, in step (2), the rotational speed of the second mixing is 500-800 rpm; And / or, the mixing time in step (2) is 3-5 hours; And / or, the heating rate of the annealing in step (2) is 1-5℃ / min; And / or, the holding temperature for annealing in step (2) is 700-900℃; And / or, the annealing time in step (2) is 4-6 hours.

6. The method for preparing the modified cathode material according to any one of claims 1-5, characterized in that, The organic carbon source in the organic carbon source solution in step (3) includes at least one of glucose, phenolic resin, and sucrose; And / or, the concentration of the organic carbon source solution in step (3) is 0.1-1 mol / L; And / or, in step (3), the mass ratio of the second intermediate product to the organic carbon source solution is 1:(1-3); And / or, the temperature of the hydrothermal reaction in step (3) is 150-200℃; And / or, the hydrothermal reaction time in step (3) is 10-15 h.

7. The method for preparing the modified cathode material according to any one of claims 1-6, characterized in that, The carbonization temperature in step (3) is 550-800℃; And / or, the carbonization time in step (3) is 3-5 hours; And / or, the carbonization atmosphere in step (3) includes a nitrogen atmosphere or an inert atmosphere.

8. A modified cathode material, characterized in that, The modified cathode material is prepared by the preparation method according to any one of claims 1-7. The modified cathode material includes a matrix material and a carbon coating layer covering the surface of the matrix material. The matrix material includes sodium, nickel, iron, manganese and zinc. The zinc in the modified cathode material is doped in a nano-network structure.

9. The modified cathode material according to claim 8, characterized in that, The chemical formula of the matrix material is Na. x Ni a Fe b Mn c Zn d O2, where 0 < x ≤ 0.85, 0 < a < 0.20, 0 < b < 0.10, 0 < c < 0.75, 0 < d ≤ 0.2, d = 1 - abc; And / or, the carbon material in the carbon coating layer is graphitized carbon material.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, and the positive electrode material includes the modified positive electrode material according to claim 8 or 9.

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